In an attempt to further increase circuit density, three-dimensional integrated circuits (3DICs) have been investigated. In a typical formation process of a 3D IC, two chips are bonded together and electrical connections are formed between each chip and contact pads on a substrate. For example, bonding two chips on top of each other. The stacked chips were then bonded to a carrier substrate and wire bonds electrically coupled contact pads on each chip to contact pads on the carrier substrate. However, this requires a carrier substrate larger than the chips for the wire bonding. More recent attempts have focused on flip-chip interconnections and the use of conductive balls/bumps to form a connection between the chip and the underlying substrate, thereby allowing high-wiring density in a relatively small package. Traditional chip stacking using solder joints involves solder, flux and underfill. All these processes created issues and limitations on pitch, joint height, and flux residue.